C++ plus

2 Goals Some general C++ tips

3 C++ Tips is header file for a library that defines three stream objects Keyboard an istream object named cin Screen an ostream object named cout an ostream object named cerr used for error reports

4 C++ Tips Insertion Operator ( << ) An output (ostream) operator that takes 2 operands –The left operand is a stream expression, such as cout –The right operand is an expression describing what to insert into the output stream cout << "The book costs" << cost;

5 C++ Tips Extraction Operator ( >> ) An input (istream) operator that takes 2 operands –The left operand is a stream expression, such as cin –The right operand is a variable of simple type Operator >> attempts to extract the next item from the input stream and store its value in the right operand variable cin >> cost; The value being keyed in for cost must be the same type as that declared for variable cost

6 C++ Tips Whitespace characters Characters such as blanks, tabs, line feeds, form feed, carriage returns, and other characters that you cannot see on the screen Extraction operator >> “skips” leading whitespace characters before extracting the input value from the stream Use function get to read the next character in the input stream cin.get(inputChar); get returns one character

7 C++ Tips #include int main( ) { using namespace std; int partNumber; float unitPrice; cout << “Enter part number followed by return: “ << endl ; // prompt cin >> partNumber ; cout << “Enter unit price followed by return: “ << endl ; cin >> unitPrice ; cout << “Part # “ << partNumber // echo << “at Unit Cost: $ “ << unitPrice << endl ; return 0; }

8 C++ Tips File input/output #include provides ofstream (output file) uses << ifstream (input file) uses >> ifstream myFile; myFile.Open("Data"); internal nameexternal name Open binds internal name to external name

9 C++ Tips ofstream yourFile; yourFile.Open("DataOut"); internal name external name yourFile.Close(); closes the file properly

10 C++ Tips Statements for using file I/O #include using namespace std; ifstream myInfile; // declarations ofstream myOutfile; myInfile.open(“A:\\myIn.dat”);// open files myOutfile.open(“A:\\myOut.dat”); myInfile.close( );// close files myOutfile.close( );

11 C++ Tips What does opening a file do? –associates the C++ identifier for your file with the physical (disk) name for the file –if the input file does not exist on disk, open is not successful –if the output file does not exist on disk, a new file with that name is created –if the output file already exists, it is erased –places a file reading marker at the very beginning of the file, pointing to the first character in it

12 C++ Tips Stream failure File enters the fail state –further I/O operations using that stream are ignored –Computer does not automatically halt the program or give any error message Possible reasons for entering fail state include – invalid input data (often the wrong type) – opening an input file that doesn’t exist – opening an output file on a diskette that is already full or is write-protected.

13 C++ Tips #include using namespace std; int main( ) {// CHECKS FOR STREAM FAIL STATE ifstream inFile; inFile.open(“input.dat”);// try to open file if ( !inFile ) { cout << “File input.dat could not be opened.”; return 1; } // rest of the program return 0; }

14 C++ Tips Reading in file names ifstream inFile; string fileName cout << "Enter the name of the input file" << endl; cin << fileName; inFile.open(fileName.c_str()); Why not just fileName?